Electrical connector and method and apparatus for making same



Oct. 6, 1970 A. M. ZAK v 3,533,055

ELECTRICAL CONNECTOR AND METHOD AND APPARATUS FOR MAKING SAME Filed March 14, 1968 4 Sheets-Sheet J.

f FIG. 5

. I ALFRED NIIQYQTRRK ATTORNEYS Oct. 6, 1970 A. M. ZAK 3,533,055

* ELECTRICAL CONNECTOR AND METHOD AND APPARATUS FOR MAKING SAME Filed March 14, 196 s 4 Sheets-Sheet 2 v I J M6 3i J 3 v .Ol85

- FIG. 9

[ 54b 56b 3 X681 46b I Fae. I ALF-REID.

ATTORNEYS Oct.6,1970 MZAK 3,533,055

ELECTRICAL CONNECTOR AND METHOD AND APPARATUS FOR MAKING SAME Filed March 14, 1968 4 Sheets-Sheet 5 INVENTOR.

ALFRED M. ZAK

' ATTORNEY$ Oct. 6, 1970 M A. M. ZAK 3,533,055

ELECTRICAL CONNECTOR AND METHOD AND APPARATUS FOR MAKING SAME Filed March 14, 1968 4 Sheets-Sheet 4 QiQQQQQ -QQQQQQ $6 "QQ,QQ/QQ "QQQ QQ QQ @Q@r;u

me //a he A A INYENTOR.

ALFREDANL'ZAK ATTORNEYS United States Patent 3,533,055 ELECTRICAL CONNECTOR AND METHOD AND APPARATUS FOR MAKING SAME Alfred M. Zak, 6110 Casmere Ave., Detroit, Mich. 48212 Filed Mar. 14, 1968, Ser. No. 713,041 Int. Cl. H011- /08, 11/08 US. Cl. 339-276 12 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for forming wire grip serrations on an electrical connector wherein a series of spaced ribs or serrations are formed on the inside or wire gripping face of the connector and spaced grooves are formed on the outer side of the connector. The teeth and grooves are formed by a punch and die arrangement wherein the punch is formed with a series of spaced grooves and the die is formed with a series of spaced projections for displacing metal into the grooves on the punch and thereby form the ribs. The spaces between the grooves on the punch preferably overlap the projections on the die so that when the punch and die are closed the metal of the strip from which the connector is formed is displaced both vertically and laterally.

This invention relates to electrical connectors and more specifically to the wire grip portions of electrical connectors.

Wire connectors, or terminals as they are sometimes called, are usuallyformed at one end with a ferrule portion in whichthe bared end of a wire is crimped. The wire grip portions are conventionally formed with a series of"transversely-extending serrations which, when the wire grip portion is crimped around the bared end of a wire (particularly a multistrand wire), are intended to embed in the wire and thus retain the connector on the end of the wire. In some instances these serrations are formed by bending the wire grip portion of the connector into zig-zag shape.-In other instances the serrations are formed by 'the mannergenerally'illustrated in US. Pat. No. 3,112,150 wherein a series of ribs are formed on the outer surface of the wire grip portion by a punching operation so that the inner or wire-gripping surface is defined by 'a series of spaced grooves aligned with the ribs.

The prior art methods of forming the wire grip portion of an electricalconnector have several disadvantagesj'The tooling employed for forming the wire grip portion is costly to fabricate and costly to maintain. The prior art tooling is subjected to wear which adversely affectsthe forming operations and which requires very precise alignment. The wire grip portions of prior art electrical connectors require relatively great crimping pressures tofhold the wire and even the relatively high crimping "pressures-employed do not result in the high pull strengths required or desired by many industrial users.

It is an object ofthis inventionto increase the wire holdingstrength of a wire connector without increasing thev size of the connector.

A furtherobject of the invention is to increase the wire holding strength of a wire connector without increasing the crimping pressures.

"Another object of the invention is to reduce the cost of tooling employed in forming the wire gripping por- ICC become apparent from the following description and drawings in which: 5

FIG. 1 is a fragmentary elevational view, partly in section, of a wire having an electrical connector formed in accordance with this invention secured to the end thereof.

FIG. 2 is a sectional view along the line 2-2 in FIG. 1.

FIG. 3 is an enlarged view of a portion of the wire grip portion of the connector illustrated in FIG. 1.

FIG. 4 is a fragmentary perspective view of a punch and die arrangement according to the present invention for forming the wire grip portion of the connector.

FIG. 5 is an elevational view of the punch illustrated in FIG. 4.

FIG. 6 is a fragmentary plan view of a strip of sheet metal stock from which the connector is formed and showing in a condensed manner progressive stages of formation.

FIG. 7 is an end view of a punch and die arrangement employed for crimping the connector on the bared end of a wire.

FIGS. 8, 9, 10, 11 and 12 are views illustrating different punch and die arrangements according to the present invention which may be utilized for forming the wire grip portion of the connector and also illustrating the cross sectional configuration of the wire grip portion resulting from the use of such punches and dies.

FIG. 13 is a perspective view of a modified form of die section according to the present invention.

FIG. 14 is a fragmentary plan view of the wire grip portion of an electrical connector formed by utilization of a die section such as shown in FIG. 1'3.

FIG. 15 is a sectional view along the line 1515 in FIG. 14.

FIG. 16 is a sectional view along the line 16-16 in FIG. 14.

FIG. 17 is a sectional view along the line 17-17 in FIG. 14.

FIG. 18 is a fragmentary sectional view showing a wire grip serration on an electrical connector of conventional construction.

In FIG. 1 a female electrical connector, generally designated 10, is formed at one end with a cylindrical barrel portion 12 for receiving the cylindrical barrel portion 14 of a male connector 16. Connector 10 is formed at its other end with a wire grip portion 18 and an insulation grip portion 20. Such connectors are usually formed in a progressive die assembly from a strip of resilient sheet metal such as brass. A strip of such metal, designated 22, is shown in FIG. 6. As the strip 22 is fed through the successive stations of the progressive die assembly in the direction of the arrow in FIG. 6, it is initially formed with a series of indexing pin holes 24. The connector is then blanked from the strip to the configuration shown at 26 after which the serrations 28 are formed in the wire grip portion at a successive station. At a further station the wire grip portion 18 and the insulation grip portion 20 are bent into U-shape as indicated at 30 to receive the end of a wirefThe connectors remain attached to the continuous edges of strip 22 by lugs 31 so that they may be wound into a coil (not illustrated) from which they are severed when the connectors are eventually crimped on the bared ends of wires.

In the showing in FIG. 6 only those'operations relating to the wire grip portion 18 and the insulating grip portion 20 are illustrated. As a consequence, in actual practice there are one or more stations in the die assembly between the blanking station and the station that forms the serrations 28 and one or more stations between the serration forming station and the station in which the wire grip and insulating grip portions are formed into U-shape.

A portion of the station of a progressive die assembly at which the serrations 28 are formed is generally illustrated in FIG. 4. The vertically reciprocating punch assembly comprises a punch retainer 32 in which a rectangular cavity 34 is ground for receiving a punch member 36 with an insert side plate 38 at each side thereof. The stationary die assembly at the wire grip forming station comprises a dieretainer 40 in which a rectangularly-shaped cavity 42 is ground for receiving a composite die comprising a die block 44 which is slotted to receive a die member 46. Cavity 42 also receives a die block 48 for initially forming the insulating grip portion 20 of the connector. Adjacent each side of cavity 42 die block 44 is fashioned with inclined abutments 50 for coining the opposite lateral free edges of wire grip portion 18. Die block 48 is fashioned with similar abutments 52 for coining the opposite free lateral edges of the insulating grip portion 20.

Die member 46 is in the form of a blade fashioned with a series of spaced, rectangularly-shaped teeth 54 separated by a series of rectangularly-shaped grooves 56 ground into the upper end of the blade. Teeth 54 protrude upwardly above the top flat reference face 58 of the die; or, stated differently, teeth 54 protrude upwardly above die level. Punch member 36 has a series of rectangularly-shaped grooves 60 ground into the lower end thereof which are separated by rectangularly-shaped teeth 62. The lower end faces 61 of teeth 62 are flush with the lower flat reference face '63 (FIG. 8) of the punch. When the various punch and die components are assembled as shown in FIG. 4, teeth 54 form a series of spaced projections which protrude above the die level 58 and grooves 60 form a series of spaced cavities in the flat reference surface 63 of the punch assembly.

In view of the manner in which the serrations are formed on the wire grip portion of the connector in accordance with the present invention, punch member 36 which, as illustrated in FIG. 4, is also in the form of a rectangularly-shaped blade may be made substantially wider than die blade 46 and may be formed with a series of teeth 62 at each of the four corners thereof (FIG. for a purpose explained more fully hereinafter.

Referring now to FIG. 8, there is illustrated a preferred configuration and relative disposition of punch and die blades in accordance with the present invention. As illustrated in FIG. 8, on the punch member 36 the width of each tooth 62, designated D, is approximately the same or slightly less than the width, designated C, of each groove 60. Likewise, in the die blade 46- the width, designated G, of each tooth 54 is generally equal to or slightly less than the width, designated H, of each groove 56. Preferably each tooth 62 on punch member 36 overlaps approximately one-half of each tooth 54 on die blade 46. In other words, in the arrangement shown in FIG. 8 the dimension A equals the dimension 0. The sheet metal strip 22 is illustrated as having a thickness M.

When the punch and die are closed on the strip 22 portions of the metal strip are squeezed between the overlapping portions of the teeth 62 on the punch and the teeth 54 on the die. The squeezed metal flows laterally as Well as vertically into grooves 60 on the punch member 36 and grooves 56 on the die member 46 so that the serrations on the upper or Wire engaging surface of the connector are defined by a series of upwardly projecting ribs 64 separated by grooves 66. On the lower or outer face of the connector the serrations 28 are defined by a series of grooves 70 separated by ribs 68-.

When the punch and die arrangement illustrated in FIG. 8 is employed as shown, the top faces 72 of ribs 64 slope inwardly toward the plane of the metal in the direction to the left which is the wire end of the connector; that is, the right hand end of the connector as viewed in FIG. 1. These inwardly sloping surfaces terminate at their upper end in a crest 74. The trailing side faces of ribs 64 are angled downwardly or inwardly as at 4 76 at a relatively steep angle. As shown in FIG. 8, ribs 68 on the lower or outer face of the terminal have a configuration generally the reverse of ribs 64.

In FIG. 8 the final thickness of the wire grip portion between ribs 64 is designated B; the height of ribs 64 is designated F; and the depth of grooves 70 is designated I. While theoretically the punch 36 can be driven downwardly to an extent such that the punch and die are closed completely on the metal strip, in practice, due to the resistance of the metal and its resilience, a clearance R will result between the lower face of the strip 22 and the top reference surface 58 of die member'46.

Since the dimension A represents the portion of each tooth 54 of the die which is not overlapped by a tooth 62 on the punch, it follows that if the dimension A is increased then the dimension K is decreased and the slope of the top face 72 of ribs 64 will be less. As will be explained more fully hereinafter, it is preferred to have an appreciable slope on the top face 72 of each rib 64 and a substantial mass of metal in each rib 64. Optimum results have been obtained when dimension A is equal to approximately one-half of the Width of the groove 60 in punch member 36; that is, approximately one-half of the dimension C as shown in FIG. 8, and the dimension A equals dimension 0. Also in the preferred arrangement the width of teeth 62 and 54 are substantially equal to the width of grooves 60 and 56; that is, dimensions C, D, G and H are substantially equal.

The height of the ribs 64 are in part determined by the dimension B. Preferably the ribs should have a height approximately one-third of the wire diameter in the case of a multi-strand wire. If the height of the ribs 64 is too great the ribs may impose too great a stress on the wire strands when the connector is crimped on a wire. Likewise, if the rib height is too great, the thickness of the connecting portions 78, that is the dimension B, will be decreased to a point of impairing the strength of the wire grip portion. The depth of grooves 60, that is dimension L, should never be more than necessary to clear the tops of the ribs formed by displacement of metal into grooves 60. An excessive L dimension will merely weaken the teeth 62. Likewise, an excessive E dimension will merely weaken the teeth 54 on the die. The depth of the grooves on the outer or lower face of the connector, that is the dimension I, will in the arrangement illustrated in FIG. 8 correspond generally to the height of the ribs 64 on the top or inner face of the connector. The dimension J is not critical.

It must be appreciated that the parts are illustrated in FIG. 8 on a highly enlarged scale. For example, assuming the metal strip 22 has a thickness of about .0125" in the arrangement shown in FIG. 8, the height of ribs 64 (that is the dimension F) is only about .0036" while the width of these ribs (dimension C) is only about .013".

The arrangement illustrated in FIG. 9 is similar to that shown in FIG. 8 except the sheet metal strip 22a is substantially thicker than strip 22 and the height of the ribs 64a are slightly greater than the height of ribs 64. In other respects the arrangement illustrated in FIG. 9 is substantially the same as that shown in FIG. 8. The configuration, dimensions and relative positions of punch member 36 and die blade 46 are the same as shown in FIG. 8. I

In FIG. 10 punch member 36b is formed with a series of grooves 60b separated by teeth 62b. Likewise, the die blade 46b is formed with teeth 54b and grooves 56b between the teeth. However, as distinguished from the punch and die member illustrated in FIGS. 8 and 9, in the arrangement shown in FIG. 10- grooves 60b and 56b are wider than grooves 60' and 56, respectively, and teeth 62b and 54b are narrower than teeth 62 and 54, respectively. In this arrangement ribs 64b are wider than ribs 64. However the top faces 72b of ribs 64b are inclined at a slightly lesser angle than top faces 72 of ribs 64. Since grooves 60b and 56b are wider than grooves 60 and 56, they are easier to grind but teeth 62b and 54b are weaker than teeth '62 and 54.

In FIG. 11 punch rnember 36 and die blade 46 are the same as those illustrated in FIGS. 8 and 9 but are illustrated with teeth 62 vertically aligned with teeth 54 and grooves 60 vertically aligned with grooves 56. When the punch and die are arranged in this fashion the ribs 64c and 680 are of generally the same configuration and vertically aligned. Likewise, grooves 660 are vertically aligned with grooves 7 00.

While it is preferred that the metal working faces on the ends of teeth 62 and 54 are flat, nevertheless these surfaces can be formed with a rounded contour if desired. For example, in FIG. 12 teeth 62d on punch member 36 are fashioned with a rounded corner 80 and the teeth'54d on die member 46d are likewise formed with a rounded corner 82 reversely positioned with respect to the rounded corner 80 of the opposed projection 62d. In view of these rounded corners on the punch and die members the ribs 64d are correspondingly contoured at their leading faces 76d.

In the arrangements illustrated in FIGS. 8 through 12 the teeth on the punch overlap at least a portion of the teeth on the die. This punch and die arrangement is preferred so that in the finished wire grip portion 18 there is'assurance that each rib 64 will be backed up at least in part on the outer side of the connector by a portion of a rib 68. In this respect the wire grip serration of this invention differs from the prior art type such as illustrated in FIG. 18 wherein the punch and die arrangement is such that each rib 84 on one side of the wire grip portion is vertically aligned with a groove 86 on the opposite side of the wire grip portion.

- The connector is adapted to be crimped around the end of a wire by means of the crimping tool assembly illustrated in FIG. 7 which includes a punch member 88 and a die member 90. This crimping tool assembly is of conventional design wherein the punch member 88 is fashioned with a-crimping cavity 92 and the die member 90 is fashioned with an anvil 94. When securing the connector to the end of a wire, the bared endof the wire is inserted in the wire grip portion 18 with the adjacent insulation 96 within the insulation grip portion 20. In the arrangement illustrated the wire, generally designated 98, is of the multi-strand type, each strand being designated 100. The wire is inserted in the connector and the wire grip portion is placed on the seat 102 of anvil 94. In this connection it will be'obs'erved that when the wire grip portion is formed as described the outer or bottom face of the wire grip portion is defined bythe lower face 104 .(FIG. 8) of the metal strip and the lowermost portions of ribs 68 which are generally co planar therewith. There are no protrusions on the lower or outer face of the wire grip portion. The outer face of the wire grip portion is definedessentially by a series of regularly-spaced grooves in the outer face of the sheet'metal. i

v, The inner face of a wire grip portion is defined by a plurality of inwardly projecting ribs 64. When the crimping punch 88 is brought downwardly on the wire connector with the end of the wire inserted therein, the free edges of the wire grip'portion 18 are turned radially inwardly and downwardly by the curved surfaces 106 of recess 92 so that in the crimped condition these edges, designated108, assume the position illustrated in FIG. 2. The closed crimped height, designated CCH in FIG. 2, will vary with the gauge of the wire but, in any event, must be such that a considerable pressure is exerted on the strands of wire within the wire grip portion. While this CCH dimension might vary considerably for wires in the range of 14 through gauge, the width of the crimped wire gripping portion of the terminal; that is, the dimension W in FIG. 2, may remain nearly constant.

The amount of pull that can be exerted on the connector while still retaining it on the end of the wire depends upon the gripping action or friction between the wire gripping portion 18 and the wire. In the case of a multi-strand wire it is important that both the exterior and the interior strands be subjected to considerable pressure when the connector is crimped on the end of the wire. If the interior wires are not subjected to considerable pressure there will be little frictional resistance between the surfaces of the adjacent interior wires and consequently the assembly will not be capable of withstanding tension to the desired degree because only the outer strands will be absorbing most of the load.

The wire gripping portion on a connector formed in accordance with the present invention has very marked advantages over conventionally formed wire gripping serrations in relation to the ability to subject the interior strands of the wire to considerable pressure. In a conventionally formed wire gripping serration as shown in FIG. 18, the rib 84 is formed on the exterior face of the connector and on the inner face of the connector there is located a groove 86 directly opposite rib 84. When a connector of this type is crimped around the bared end of a wire in a conventional crimping tool assembly such as shown in FIG. 7, instead of the wire embedding into the groove there is a tendency for the groove 86 to nearly wipe out. More specifically, when the rib 84 is subjected to a crimping pressure, designated by the arrow P in FIG. 18, the rib is displaced inwardly to a large extent so that its outer surface assumes the position designated 110 and the bottom of the groove 86 is displaced inwardly to the position designated 111. With this arrangement while the outer strands of the wire are embedded slightly into grooves 86, the inner strands of the wire are not subjected to any substantial pressure.

With the wire grip portion 18 of the connector formed in accordance with the present invention a much stronger connection between the connector and the wire is obtained. It will be observed that the ribs 64 define inward projections on the inner wire gripping surface of the connector. Thus, the wire strands 100 are subjected to crimping pressure much sooner when the crimping punch 88 descends. Furthermore, it will be observed that each rib 64 is backed up on the outer side of the connector by a relatively substantial mass of metal forming the opposed rib 68. This differs from conventional wire grip serrations where there is a groove directly opposite each rib. When the wire grip portion of the present invention is crimped around a wire, the crimping pressures are transmitted more directly to the interior wire strands and sooner in relatiton to the stroke of crimping punch 88. As a consequence, as shown in FIG. 3, even the wire strands 100 which are located adjacent the center of the wire are subjected to considerable pressure and are distorted so that they are in firm frictional engagement with the adjacent Wires.

When the connector of this invention is crimped on a wire the ribs 64 and 68 are flattened and reoriented to some extent as shown at 64 and 68' in FIG. 3; but, in any event, ribs 64 become embedded firmly within the outer Wire strands 100 and produce localized distortions of substantially all the wire strands. It will also be appreciated that since the portions 78 of the metal strip interconnecting the adjacent ribs 64 are of reduced thickness (dimension B in FIG. 8), the ribs 64 are readily reoriented when subjected to the crimping pressure. This also results in a better gripping acttion between ribs 64 and the strands of wire as shown in FIG. 3.

Pull tests conducted for the purpose of comparing the pull strength of the wire grip serrations of the present invention and wire grip serrations of the conventional type illustrated in FIG. 18 conclusively show that a much stronger connection is obtained with the wire grip of the present invention with less crimping pressures. For example, with the wire grip serrations of the type illustrated in FIG. 18 a pull test of 37 lbs. was obtained on 16 gauge stranded wire where the closed crimped height (CCH) was .066 and a pull test of 56 lbs. was obtained on the same wire with a closed crimped height of .060". When a connector having a wire grip portion formed in accordance with the present invention (specifically of the type shown in FIG. 8) was crimped on a 16 gauge stranded wire, a pull test of 70 lbs. was obtained with a closed crimped height of .066" and a pull test of 72 lbs. was obtained with a closed crimped height of .060". As a matter of interest, the 16 gauge wire employed itself had a tensile strength of 75 lbs. Thus, with the wire grip serrations of the present invention the connector was capable of withstanding a pull test nearly equal to the tensile strength of the Wire itself. Tests have also shown that, while the millivoltage drop resulting from a wire grip serration of the type herein disclosed is slightly greater than that obtained with a conventional wire grip serration, the increase is of such small magnitude as to be insignificant.

As mentioned previously, based on numerous tests, the configuration of the wire grip portion shown in FIG. 8 is' preferred. The wire grip section shown in FIG. 10 gives equally good results for 16, 18 and gauge wires but a slightly lesser pull strength for 14 gauge wire. The wire grip sections shown in FIGS. 11 and 12 also produce high pull strengths but have a tendency to cause a substantial increase in the width of the strip (length of the connector) which may give rise to problems in feeding the strip through successive stations.

FIG. 13 illustrates a blade type die insert 113 generally similar to that illustrated at 46 in FIG. 4 except that the teeth 54 are not formed as continuous ribs across the width of the blade but rather as a series of small teeth 112 spaced apart transversely by cross grooves 114. These individual teeth 112 are formed simply by grinding grooves 114 perpendicular to grooves 56 in the end face of blade 113. A die insert of the type illustrated in FIG. 13 will produce a wire grip portion having more undisturbed metal as compared with a wire grip portion where the ribs extend continuously across substantially the full width of the wire grip portion. The metal of the connector registering with grooves 114 is undisturbed when the punch and die are closed upon one another. This is the section of metal designated 116 in FIGS. 14 and 15. Each rib of the wire grip serration is defined by a series of spaced humps 118 extending in rows across the wire grip portion 18 rather than a rib extending continuously across the wire grip portion. In this arrangement a cavity 120 partially underlies each rib hump 118. These spaced cavities are formed by teeth 112. However, when viewed in section lengthwise of the connector, the rib formation produced by the die section illustrated in FIG. 13 does not differ substantially from the cross section shown in FIG. 8. This is evidenced by a comparison of FIG. 17 with FIG. 8. The cross channels or cross grooves 114 may be formed if desired on the punch member or on both the punch and die members. In either case since less metal in the strip is deformed, the pull strength of the connector will be somewhat less than that obtainable where the ribs extend continuously across the wire grip portion and where the closed crimped height remains the same. However even with the type of die section shown in FIG. 13 the pull strength is substantially increased over that obtainable with the conventional wire grip serration shown in FIG. 18 and can be increased by decreasing the closed crimped height.

The die arrangement illustrated in FIG. 13 permits the formation of deeper ribs and thinner connecting portions between the ribs. The deeper ribs result in deeper penetration into the wire for the same crimp height and therefore adapts the connector for use with heavier gauge wire.

The tooling required for forming a wire grip serration according to the present invention can be produced economically. The punch member 36 can be formed as a blade wherein the grooves 60 are ground directly across the edge of the blade rather than being formed as a cavity. It is true that grinding a tooth in this fashion produces a tooth structure which is somewhat weaker than where the cavity between adjacent teeth is formed by a hobbing operation. However in the metal displacing operation according to the present invention the teeth in the punch and die are not subjected to excessive lateral pressures. Thus, forming these teeth by a grinding operation is not objectionable. For example, referring to FIG. 8, in the present arrangement when the punch and die are closed upon the strip of metal, the metal flows freely in a lateral as well as a vertical direction and the teeth of the punch and die members are not subjected to any substantial lateral pressure. The metal flows freely into the grooves between the successive teeth. The ribs are formed substantially freely in the grooves of the punch and die and there is no tendency for the workpiece to seize on the tools. Therefore, there is no excessive side thrust which would have a tendency to break the teeth. As a result the punch and die members of the apparatus described are not subjected to nearly as much wear as in conventional tooling for forming wire grip serrations of the type illustrated in FIG. 18. For this reason the punch and die members can be formed as blades with teeth ground therein.

It will also be observed that with the arrangement illustrated and described herein there need not be perfect alignment between the punch and die sections as is the case with tooling used for forming the conventional wire grip serrations. For example, the rib formation shown in FIG. 8 is not appreciably altered if the punch is shifted slightly relative to the die. With the present invention, since punch member 36 is formed as a blade and arranged in retainer 32 with insert plates 38 at each side thereof, teeth 62 can be ground at all four corners of the blade as shown in FIG. 5. As the teeth wear, the blade can simply be re-oriented to present all four corners successively to the metal strip. Furthermore, even with substantial wear on the teeth of the punch and die the formation of the desired rib configuration is not substantially impaired.

Another advantage from the tooling standpoint of forming the wire gripping rib on the inside of the wire grip portion rather than on the outside resides in the fact that when the rib is formed on the outside each successive station in the progressive die assembly must have clearance ground into the lower die section in order to accommodate the outwardly or downwardly projecting rib. The grinding of such clearances in die sections not only weakens them but also creates numerous problems in connection with sharpening the dies. As mentioned previously, the provision of an interior serration or rib also results in a greater pressure being tansmitted to the interior wire strands at a lesser crimping height to create a better holding power with less strain on the crimping tooling. Thus, the provision of the interior rib also results in economy from the standpoint of maintaining the tools for crimping the connector on the wires. Economies in relation to the cost of crimping tooling are also achieved by reason of the fact that tests have shown that the same crimping tooling and the same connectors are suitable for use with 14, 16, 18 and 20 gauge wires by merely adjusting the crimp height.

In forming the wire grip serrations in accordance with the present invention metal is caused to flow freely to provide the rib formation. The metal adjacent each rib is not subjected to the severe stresses which result from the formation of a wire grip serration of the type illustrated in FIG. 18. Thus with the present invention there is less tendency for the metal to fracture. The wire grip serrations can thus be spaced closer together to provide more serrations per unit length of connector. The serrations can be extended across substantially the full width 9 of the wire grip portion 18 so that when it is crimped around a wire the inwardly projecting ribs extend almost completely around the periphery of the group of strands forming the wire.

A further advantage of the wire grip according to the present invention is that the free end of the bared wire need not extend outwardly beyond the inner end of the wire grip portion in order to result in a high pull strength. In FIG. 1 it will be noted that the ends of wire strands 100 extend outwardly beyond the wire grip portion at 122 and that these wire ends as a group are radially expanded relative to the crimped portion of the wire. In an electrical connector having a conventional wire grip portion the pull strength is lower if the ends of the wire strands terminate within the wire grip portion rather than beyond it. In a conventional electrical connector the resistance offered by the expanded ends of the wire is relied upon to a degree to achieve the desired pull strength. With the wire grip portion of the connector formed as disclosed herein the pull strength is substantially unaffected by the fact that the wire ends do not extend outwardly beyond the wire grip portion.

I claim:

1. An electrical connector comprising a sheet metal body having a wire retaining end provided with a wire grip portion of generally U-shape, said wire grip portion being adapted to receive the bared end of a wire and to be crimped thereon by turning the ends of the U inwardly and pressing them toward the bight portion of the U, said wire grip portion having an inner wire engaging face and an outer face, a series of transversely extending ribs on each of said faces, said ribs being spaced apart lengthwise of the wire grip portion with the spaces therebetween defining grooves, the grooves on one of said faces at least partially overlapping the grooves on the other face in a direction lengthwise of the wire grip portion and the ribs on one face at least partially overlapping the ribs on the other face in a direction lengthwise of the wire grip portion, the grooves and ribs on each face being staggered and asymmetrical relative to the ribs and grooves, respectively, on the opposite face in a direction lengthwise of the wire grip portion, the metal sections between the overlapping portions of the grooves forming a connection between laterally adjacent ribs which is thinner than said sheet metal.

2. An electrical connector as called for in claim 1 wherein the ribs on one of said faces protrude from said face with the bottoms of the grooves therebetween being substantially flush with said one face, the ribs on the other face having their outermost surfaces substantially flush wtih said other face with the bottoms of the grooves therebetween being depressed into said other face.

3. An electrical connector as called for in claim 1 wherein the ribs on said wire engaging face project inwardly from said wire engaging face and the bottoms of the grooves between the last-mentioned ribs are substantially flush with said inner wire engaging face, the outer end faces of the ribs on the outer face of the wire grip portion being substantially flush with said outer face and the bottoms of the grooves in the outer face being offset inwardly of said outer face.

4. An electrical connector comprising a sheet metal body having a wire retaining end provided with a wire grip portion of generally U-shape, said wire grip portion being adapted to receive the bared end of a wire and to be crimped thereon by turning the ends of the U inwardly and pressing them toward the bight portion of the U, said wire grip portion having inner and outer faces, a series of transversely extending ribs on each of said faces, said ribs being spaced apart lengthwise of the wire grip portion with the spaces therebetween defining grooves, the grooves on one of said faces at least partially overlapping the grooves on the other face in a direction lengthwise of the Wire grip portion and each rib on one face overlying approximately half of the juxtaposed rib on the opposite face in a direction lengthwise of the wire grip portion, the metal sections between the overlapping portions of the grooves forming a connection between laterally adjacent ribs which is thinner than said sheet metal.

5. An electrical connector as called for in claim 4 wherein each groove on said opposite face overlies approximately one-half of the juxtaposed groove on said one face.

6. An electrical connector comprising a sheet metal body having a wire retaining end provided with a wire grip portion of generally U-shape, said wire grip portion being adapted to receive the bared end of a wire and to be crimped thereon by turning the ends of the U inwardly and pressing them toward the bight portion of the U, said wire grip portion having inner and outer faces, a series of transversely extending ribs on each of said faces, said ribs being spaced apart lengthwise of the wire grip portion with the spaces therebetween defining grooves, the grooves on one of said faces at least partially overlapping the grooves on the other face in a direction lengthwise of the wire grip portion and the ribs on one face at least partially overlapping the ribs on the other face in a direction lengthwise of the wire grip portion, the metal sections between the overlapping portions of the grooves forming a connection between laterally adjacent ribs which is thinner than said sheet metal, the transversely extending ribs on one of said faces being interrupted along their length by depressed sections which define grooves extending lengthwise of the wire grip portion.

7. An electrical connector comprising a sheet metal ferrule crimped around the bared end of a wire, said ferrule having a series of spaced inwardly protruding ribs on the inner side thereof which extend around the inner periphery of the ferrule and are separated by grooves, the outer surface of the ferrule having a plurality of spaced grooves therein which extend around the outer periphery of the ferrule and are spaced apart to form a plurality of ribs therebetween, the outer faces of the last-mentioned ribs being substantially flush with the outer surface of the sheet metal formig the ferrule and the radially inner faces of the first-mentioned ribs being spaced radially inwardly of the inner surface of the sheet metal forming the ferrule, each of said outer ribs overlapping approximately half of the opposed inner rib and being axially oifset from the adjacent groove on the inner surface of the ferrule.

8. An electrical conductor comprising a sheet metal ferrule having a wire retaining end provided with a wire grip portion of generally U-shape; said wire grip portion having an inner wire engaging surface; said wire engaging surface having a radially distorted portion surrounded by a generally smooth portion; said distorted portion being defined by a series of ribs spaced apart lengthwise of the wire grip portion; said ribs protruding inwardly from said wire engaging suface and extending around the inner periphery of said wire grip portion; said ribs being separated by grooves; the outer surface of the wire grip portion having a plurality of spaced grooves recessed therein which extend around the outer,

periphery of the wire grip portion and are spaced apart lengthwise thereof to form a plurality of ribs therebetween; the outer faces of the last-mentioned ribs being substantially flush with the outer surface of the sheet metal forming the wire grip portion and the bottoms of the first-mentioned grooves being substantially flush with said smooth, undistorted portion of said inner wire engaging surface; the grooves on one of said surfaces at least partially overlapping the grooves on the other surface in a direction lengthwise of the wire grip portion and the ribs on one surface at least partially overlapping the ribs on the other surface in a direction lengthwise of the wire grip portion; the grooves and ribs 011 each surface being staggered and asymmetrical relative to the ribs and grooves, respectively, on the opposite surface in a direction lengthwise of the wire grip portion; the

metal sections between the overlapping portions of the grooves forming a connection between laterally adjacent ribs which is thinner than said sheet metal.

9. An electrical connector as called for in claim 8 wherein the outer peripheral portions of said wire are curved radially inwardly at the axial portions thereof adjacent said inner ribs.

10. An electrical connector as called for in claim 8 wherein said wire is of the multi-strand type, the peripherally outer strands being curved radially inwardly at the portions thereof adjacent said inner ribs and the interior strands having a curved configuration to conform generally to the axial configuration of the radially outer strands.

11. An electrical connector comprising a sheet metal body having a Wire retaining end provided with a wire grip portion of generally U-shape; said wire grip portion having an inner wire engaging surface and an outer surface; said wire engaging surface having a radially distorted portion surrounded by a generally smooth undistorted portion; said distorted portion being defined by a series of ribs spaced apart lengthwise of the wire grip portion; said ribs protruding inwardly from said inner wire engaging surface and extending around the inner periphery of said wire grip portion; said ribs being separated by grooves; the outer surface of the wire grip portion having a plurality of spaced grooves recessed therein which extend around the outer periphery of the wire grip portion and are spaced apart lengthwise thereof to form a plurality of ribs therebetween; the outer faces of the last-mentioned ribs being substantially flush with the outer surface of the sheet metal forming the wire grip portion and the bottoms of the first-mentioned grooves being substantially flush with said smooth, undistorted portion of said inner wire engaging surface.

12. An electrical connector as called for in claim 11 wherein the volume of the metal forming said ribs corresponds to the volume of the grooves in the outer surface of the wire grip portion.

References Cited UNITED STATES PATENTS 3,020,520 2/1962 Berg 339-273 3,112,150 11/1963 Hammell 339276 3,293,355 12/1966 Gropp et a1 174-84 RICHARD E. MOORE, Primary Examiner J. H. MCGLYNN, Assistant Examiner US. 'Cl. X.R. l74-84, 94 

